question about microcontroler oscillator

[Ryan Weihl]

Don McKenzie wrote:

robb wrote:
saga continues,
my repair project device uses a phillips MAB 8051 AH
microcontroller.

while trying to isolate trouble with a badly shaped clock signal
i happened across microcontroller oscillator.

the oscillator CSA 12.00 MT has a slightly warped sine wave out
of one side and a very bad dent in the crest of the sine wave on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave ?
and same on both sides ?

oscillator is connected exactly as 8051 datasheet recommends,
with the two pins from the oscillator each to small caps which
connect to 0v ref


thanks for any help,
robb

doesn't sound like a good waveform for micro operation.

http://www.intel.com/design/mcs51/applnots/23065901.pdf
have a look at page 13, this is what the original data sheets specify
for 8051's.

Don...

Don, are you using the ground clip at the probe?
long ground leads distort the picture.
rw

--

 

[TT_Man]

the oscillator CSA 12.00 MT has a slightly warped sine wave out
of one side and a very bad dent in the crest of the sine wave on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave ?
and same on both sides ?

So cut to the chase,...... does the thing you're working on not work? Have
you checked the reset pin is working correctly?

 

[Pieter]

On Tue, 30 Oct 2007 09:38:28 -0500, "robb" <some@where.on.net> wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:47271FD7.53D44280@hotmail.com...


TT_Man wrote:

If you are seeing 3-4 volts swing on one of the pins, then I
would say the
resonator is working ok. Don't worry too much about the
wiggle in the
waveform.

Yes, it'll be around 3-4 V pk-pk on one pin (Osc 2 ?) and about
a couple of
hundred mV on the other one.


well i am seeing about 4 volts on one side (the 33 pF side)
and about 3.8 volts on the (15pF) side ?

so does that mean i have a problem ?

this 8051 chip supposedly has and internal oscillator ? why would
that not be used ?
i mean is there a reason one would not use internal oscillator if
there were one.

thanks for all the help everyone, it helps me learn,
robb

The 8051 does not have an internal oscillator. But the chip is very
reliable and does not often give oscillation problems. You could check
the board for decoupling problems, that may influece things.

Pieter

 

[robb]

"TT_Man" <Someone@ntlworld.com> wrote in message
news:AOIVi.747$pg.400@newsfe6-win.ntli.net...

the oscillator CSA 12.00 MT has a slightly warped sine wave
out
of one side and a very bad dent in the crest of the sine wave
on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave
?
and same on both sides ?

So cut to the chase,...... does the thing you're working on not
work? Have
you checked the reset pin is working correctly?


thanks for reply,

good question, functions somewhat but not acceptable, so no ,
there seems to be some sluggishness in the response to user
button presses, sometimes missed presses, sometimes multiple
presses are registered

the short is there appears to be a problem but nothing is
predictably repeatable ....
so, i began looking at the most immediate source of trouble with
button presses and found that the clock signal was malformed with
ringing 1-2 volts out before settling about 1/3 accross square
(pic of signal posted in "alt.binaries.schematic.electronics" )

so following the circuit to the clock source led me back to 8051
and i am still trying to deteermine where the problem with
ringing is coming from

This is learning exercisize as i am amateur electronics
troubleshooter

i will check how reset pin is connected

thanks for help,
robb

 

[robb]

"Pieter" <dit3_werkt_ook_niet@hotmail.com> wrote in message
news:uvmei398285klllrtndrohgt3cikp2o9md@4ax.com...

On Tue, 30 Oct 2007 09:38:28 -0500, "robb" <some@where.on.net
wrote:


"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:47271FD7.53D44280@hotmail.com...


TT_Man wrote:

If you are seeing 3-4 volts swing on one of the pins, then
I
would say the
resonator is working ok. Don't worry too much about the
wiggle in the
waveform.

Yes, it'll be around 3-4 V pk-pk on one pin (Osc 2 ?) and
about
a couple of
hundred mV on the other one.


well i am seeing about 4 volts on one side (the 33 pF side)
and about 3.8 volts on the (15pF) side ?

so does that mean i have a problem ?

this 8051 chip supposedly has and internal oscillator ? why
would
that not be used ?
i mean is there a reason one would not use internal oscillator
if
there were one.

thanks for all the help everyone, it helps me learn,
robb


The 8051 does not have an internal oscillator. But the chip is
very
reliable and does not often give oscillation problems. You
could check
the board for decoupling problems, that may influece things.

Pieter

thanks for help Pieter,

everytime i read your posts i feel like a professor has given me
a research assignment
so now to read up un decoupling

thanks
robb

 

[robb]

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns99D99B0E4D4E9zoodlewurdle@140.99.99.130...

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote in
news:47271F9B.673DD522@hotmail.com:


Lostgallifreyan wrote:

"robb" <some@where.on.net> wrote

they described using a
*MOSFET buffer* to view the signals on o-scope

I was thinking of that before I saw it. Look at the thread
above this
one called "Search OpAmp chip as a voltage follower" for a
description of using a FET to buffer a high impedance
source. That
same idea will let you get a look at that waveform without
disturbing
it much. The FET and a single resistor to a stable DC rail
should be
all you need, then scope the FET output signal.

A FET input probe is NOT required to look at the
8051oscillator for
routine purposes. A 10x probe is fine.

Graham



Didn't say it was necessary. So long as the wave crosses the
zero point
regularly enough to make the timer work who cares what shape it
is? Nothing
much routine about this anyway, the guy's new to it and wants
to be sure of
what he sees.

you have pegged it exactly with just wanting peace of mind and
some learning experience

i could be reading forever.... sometimes you just have to get in
and do it to learn which id what i am doing.

I was just pointing out a useful similarity with another post.
If someone
wants to learn, there's no doubt that adding a FET and a
resistor and a DC
cource is a neat way of making sure a signal involving small
capacitances
might be less disturbed than by loading it directly with a
cable
connection. It's not a question of whether it's necessary, but
whether or
not it's useful. Robb wants to learn, so that's a good cheap
way to do it.
It would confirm that the waveform really is as he sees it, and
that it's
not being changed by his connection to it.

and that is exactly what i plan to do (build a mosfet buffer that
is) because it sounds interesting, useful and fun and good way to
learn

as long as i do not blow up my project in the process.

right now i am at the point of just check everything big and
question anything unexpected.

thanks for all the help,

robb

 

[robb]

"LVMarc" <LVMarc@att.net> wrote in message
news:11IVi.24296$bO2.22228@newsfe10.phx...

robb wrote:
saga continues,
my repair project device uses a phillips MAB 8051 AH
microcontroller.

while trying to isolate trouble with a badly shaped clock
signal
i happened across microcontroller oscillator.

the oscillator CSA 12.00 MT has a slightly warped sine wave
out
of one side and a very bad dent in the crest of the sine wave
on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave
?
and same on both sides ?

oscillator is connected exactly as 8051 datasheet recommends,
with the two pins from the oscillator each to small caps
which
connect to 0v ref


thanks for any help,
robb



problem with most probed uP oscillator studies, is:

the capacitance of the probe is about the same as capactiane of
the
oscillator,

so like hiesenberg, when you look a the clock, you effect it by
looking
with the probe. try a non contact probe and then see the real
clock
output shape(but not the corectd amp,itude), to get amplitude
you need
to correct the raw non contact data and rescale to measure the
amplitude.

Good luck with the measurent

thanks marc,

i will need to read about non-contct probe , is it something i
can make ??
pointy small 30 awg wire wilth tiny loop perhaps ?

thanks again for help,
robb

 

[Eeyore]

Pieter wrote:

The 8051 does not have an internal oscillator.

What do you mean ? It has an inverter stage designed for clock oscillator use
connected to pins xtal1 and xtal2.

Graham

 

[Lostgallifreyan]

"robb" <some@where.on.net> wrote in
news:13ieq15h71s8t3c@corp.supernews.com:

i will need to read about non-contct probe , is it something i
can make ??
pointy small 30 awg wire wilth tiny loop perhaps ?

MOSFET. That's non-contact, sort of, the gate is insulated. Has
capacitance though, but not critical to this.

That's not what was actually meant though, in this case it means a very
sensitive input, so sensitive it can pick up the signal without being close
enough to load it. Trouble with that is, it might pick up noise from other
stuff nearby. I'd go with the FET. Useful tool to keep around.

 

[Pieter]

On Tue, 30 Oct 2007 18:07:04 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

Pieter wrote:

The 8051 does not have an internal oscillator.

What do you mean ? It has an inverter stage designed for clock oscillator use
connected to pins xtal1 and xtal2.

Graham

No internal crystal. It has the inverter etc, but always needs an
external crystal. Of course you can also feed it with an external
oscillator.

Regards,
Pieter

 

[Pieter]

On Tue, 30 Oct 2007 13:14:48 -0500, "robb" <some@where.on.net> wrote:

"Pieter" <dit3_werkt_ook_niet@hotmail.com> wrote in message
news:uvmei398285klllrtndrohgt3cikp2o9md@4ax.com...
On Tue, 30 Oct 2007 09:38:28 -0500, "robb" <some@where.on.net
wrote:


"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:47271FD7.53D44280@hotmail.com...


TT_Man wrote:

If you are seeing 3-4 volts swing on one of the pins, then
I
would say the
resonator is working ok. Don't worry too much about the
wiggle in the
waveform.

Yes, it'll be around 3-4 V pk-pk on one pin (Osc 2 ?) and
about
a couple of
hundred mV on the other one.


well i am seeing about 4 volts on one side (the 33 pF side)
and about 3.8 volts on the (15pF) side ?

so does that mean i have a problem ?

this 8051 chip supposedly has and internal oscillator ? why
would
that not be used ?
i mean is there a reason one would not use internal oscillator
if
there were one.

thanks for all the help everyone, it helps me learn,
robb


The 8051 does not have an internal oscillator. But the chip is
very
reliable and does not often give oscillation problems. You
could check
the board for decoupling problems, that may influece things.

Pieter

thanks for help Pieter,

everytime i read your posts i feel like a professor has given me
a research assignment
so now to read up un decoupling

thanks
robb

Check the decoupling capacitors.

Pieter

 

[TT_Man]

So cut to the chase,...... does the thing you're working on not
work? Have
you checked the reset pin is working correctly?


thanks for reply,
good question, functions somewhat but not acceptable, so no ,
there seems to be some sluggishness in the response to user
button presses, sometimes missed presses, sometimes multiple
presses are registered

the short is there appears to be a problem but nothing is
predictably repeatable ....
so, i began looking at the most immediate source of trouble with
button presses and found that the clock signal was malformed with
ringing 1-2 volts out before settling about 1/3 accross square
(pic of signal posted in "alt.binaries.schematic.electronics" )

Are you using Port 0? Do you have pull-ups on all the pins on Port 0? That's
a common beginner mistake..
Without them, strange illogical things happen.....

 

[Eeyore]

Pieter wrote:

Eeyore wrote:
Pieter wrote:

The 8051 does not have an internal oscillator.

What do you mean ? It has an inverter stage designed for clock oscillator use
connected to pins xtal1 and xtal2.


No internal crystal. It has the inverter etc, but always needs an
external crystal. Of course you can also feed it with an external
oscillator.

Can you provide an example of any IC that has an internal crystal ?

Graham

 

[Eeyore]

TT_Man wrote:

Are you using Port 0? Do you have pull-ups on all the pins on Port 0? That's
a common beginner mistake..

It's not HIS design. It's a commercial one.

Graham

 

[Roger Hamlett]

On Tue, 30 Oct 2007 22:59:20 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

Pieter wrote:

Eeyore wrote:
Pieter wrote:

The 8051 does not have an internal oscillator.

What do you mean ? It has an inverter stage designed for clock oscillator use
connected to pins xtal1 and xtal2.


No internal crystal. It has the inverter etc, but always needs an
external crystal. Of course you can also feed it with an external
oscillator.

Can you provide an example of any IC that has an internal crystal ?

Graham
Not crystals, but many of the small microcontrollers have trimmed RC

oscillators internally, allowing them to be used for 'low accuracy'
applications, without any external oscillator.
There have been a couple of hybrid chip modules marketted in the past
with crystals included, but I don't know if any currently offer this.

Best Wishes

 

[JW]

On Tue, 30 Oct 2007 22:59:20 +0000 Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote in Message id:
<4727B747.6364ECA6@hotmail.com>:

Can you provide an example of any IC that has an internal crystal ?

Sure:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4984

 

[Eeyore]

Pieter wrote:

Check the decoupling capacitors.

I'd love to know how he's going to CHECK capacitors ! You certainly say some
daft things.

He might REPLACE any supply decoupling caps that are electrolytic types for
sure. Age is likely to have taken their toll on them.

Graham

 

[Eeyore]

Roger Hamlett wrote:

Eeyore wrote:
Pieter wrote:
Eeyore wrote:
Pieter wrote:

The 8051 does not have an internal oscillator.

What do you mean ? It has an inverter stage designed for clock oscillator use
connected to pins xtal1 and xtal2.

No internal crystal. It has the inverter etc, but always needs an
external crystal. Of course you can also feed it with an external
oscillator.

Can you provide an example of any IC that has an internal crystal ?


Not crystals, but many of the small microcontrollers have trimmed RC
oscillators internally, allowing them to be used for 'low accuracy'
applications, without any external oscillator.

Yes, I'm aware of that. To be honest, I'm being critical of Pieter who is introducing
pointless irrelevancies.

There have been a couple of hybrid chip modules marketted in the past
with crystals included, but I don't know if any currently offer this.

Exactly, hybrids not ICs. A very distinct difference that you for one are aware of.

Graham

 

[Eeyore]

JW wrote:

Eeyore wrote

Can you provide an example of any IC that has an internal crystal ?

Sure:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4984

Whilst the data sheet doesn't make it obvious, that's a HYBRID, not an IC.

Graham

 

[Pieter]

On Wed, 31 Oct 2007 12:10:54 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

JW wrote:

Eeyore wrote

Can you provide an example of any IC that has an internal crystal ?

Sure:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4984

Whilst the data sheet doesn't make it obvious, that's a HYBRID, not an IC.

Graham

So what? The point is that some parts have internal oscillators, not
just the inverters etc for external crystals, resonators or RC's.
Microchip etc.

Pieter